1. Field of the Invention
The present invention generally relates to a semiconductor device and a method of forming the same.
Priority is claimed on Japanese Patent Application No. 2008-037575, filed Feb. 19, 2008, the content of which is incorporated herein by reference.
2. Description of the Related Art
In recent years, there has been the requirement for further increase in the density of semiconductor devices. To realize highly dense semiconductor devices, it has been proposed to reduce the area of a semiconductor chip and to increase the share rate of semiconductor cells. To realize reduction in the area of a semiconductor chip and increase the cell share rate, it would be effective to narrow the width of the well isolation region that separates the p-well region and the n-well region from each other.
For example, Japanese Unexamined Patent Application, First Publications, Nos. 2007-227920, 2001-144276, 2006-237208, and 09-102586 each address a method of forming a well isolation region with a wider width, which is shallower than well layers or diffusion layers.